Phonograph apparatus



Jan. 19, 1960 Filed Oct. 3l, 1955 J. D. BCK

PHONOGRAPH APPARATUS 2 Sheets-Sheet 2 Mmmm@ www vi INVENTOR.

ATTORNEY United States Patent() PHONOGRAPH APPARATUS .lohn D. Bick,Moorestown, NJ., assignor to Radio Corporation of America, a corporationof Delaware Application October 31, 1955, Serial No. 543,960

The terminal fifteen years of the term of the patent to be granted hasbeen disclaimed 18 Claims. (Cl. 179-109.4)

The present invention relates to phonograph apparatus, and moreparticularly to an automatic control system for phonograph apparatusthat operates to prevent repeated tracking by the phonograph pickup ofthe same groove on a record.

Disc records are commonly used with automatic record changing machineswhich play a large number of records successively. A defect in any onerecord, which may cause repetitive reproduction of the same groove, isvery annoying to the listener. Known automatic record changingmechanisms do not operate until the end of a record. Therefore, in theevent of a repeated groove, a manual adjustment must be made in order topermit the usual record changing cycle. This may cause a great deal ofinconvenience to the listener.

Disc records form a large part of the daily radio broadcasting programschedule. It is desirable to play a large number of records, one afterthe other without the need for a disc-jockey attendant. Unattendedbroadcast studios where automatic machinery plays an entire days programof recorded music is an ultimate objective. Repeated tracking of thesame groove on any record in any unattended record reproduction systemmay produce disasterous consequences. The same groove will play over andover again, for an unlimited time, unless some means are provided torectify the condition.

In accordance with the invention, an automatic control system isprovided which prevents the repeated tracking of the same groove on agrooved record, such as the conventional disc record. 'There is provideda separate control channel which receives the signal from the phonographpickup. This signal is delayed for a specified time equal to the timerequired for the same groove on the record to repeat. One means foreifecting this delay is to magnetically record the signal on a recordingmedium, such as magnetic tape. The delayed signal is reproduced afterthe speciiied time interval which will be equal to the period of onerevolution of the record in most instances. Therefore, two signals areavailable. These signals would correspond to the sound recorded inconsecutive grooves on the disc record during normal recordreproduction. The delayed signal is compared with the signal enteringthe control channel. If the signals are identical for a given period, itwill reveal that the same groove has repeated, and an error signal maybe supplied to actuate suitable mechanism for counteracting thecondition. This may be done by advancing the pickup arm, for example.

In one form of the invention,v a pair of magnetic reproducing devicesare used with a looped magnetic recording medium that is rotated at aconstant velocity. These reproducing devices are spaced along the loopso that the simultaneous reproduction of signals from consecutivegrooves on the record will result. Means may be provided to erasesignals recorded on the magnetic recording medium after reproduction byboth reproducing devices. The signal output from each of the magneticreproducing devices may be transmitted through envelope detectors toprovide two signal outputs that-are proportional to the Patented Jan.19, 1960 ICC envelopes of the recorded signal. These two signal outputsmay be compared to determine if the magnetically reproduced signals areidentical over a given time period that is indicative of a repetition ofthe same groove on the disc record. If it is determined that the samegroove has been repeated, the phonograph pickup may be automaticallyadvanced or an alarm signal sounded.

It is an object of the present invention to provide a novel system forimproving the operation of automatic phonograph apparatus.

lt is a further object of the present invention to provide a novelsystem for automatically controlling phonograph apparatus to eliminatethe possibility of successivelyreproducing the same portion of arecorded signal.

It is a still further object of the present invention to provide a novelsystem for the elimination of repeated tracking of the same grooveduring record reproduction that is responsive to the output signal fromthe pickup device in phonograph apparatus. i

It is a still further object of the present invention to provide a novelsystem for automatically detecting repeated grooves during disc recordreproduction.

Other objects and advantages of the present invention will, of course,become apparent and immediately suggest themselves to those skilled inthe art to which the invention is directed from a reading of thefollowing description in connection with the accompanying drawing inwhich:

Figure 1 is a diagram, schematically showing an automatic control systemprovided by the present invention for preventing repetitive tracking ofthe same groove during disc record reproduction;

Figure 2 is a schematic diagram showing parts of the system illustratedin Figure 1 in greater detail;

Figure 3 shows representations of several signal waveforms, thewaveforms occurring in operation of the system illustrated in Figures 1and 2; and

Figure 4 is a diagram, schematically showing a modied form of the systemprovided by the present invention.

In Figure 1, a record 10 is schematically represented as being disposedupon a turntable 12. A shaft 13 drives the turntable. This shaft may beconnected to a suitable motor (not shown).

The record 10 is a disc record of the conventional type. Signals arerecorded in concentric, consecutive, spiral grooves on the record. .Apickup 14 engages and tracks the grooves. The needle on the pickup ridesin the grooves. The pickup 14 may be of any conventional design andfunctions as a transducer to reproduce the signals recorded in thegrooves into corresponding electrical output signals.

The pickup 14 is electrically connected to a signal output channel 15.This channel includes a pre-amplifier 16 that is connected to the outputterminals of the pickup 14, and an output amplifier 17 that is connectedto the output of the pre-amplifier 16. The output of the amplitier 17may be used to Voperate a loudspeakeror may be connected into the signalinput apparatus of `a radio broadcast transmitter.

The present invention is directed toward counteracting the possibilitythat the same groove on the record may repeat. To this end, a system formoving and advancing the pickup 14 in response to the occurrence of arepeated groove is provided. The signal channel 15 is ordinarily foundin record reproduction apparatus. A signal is derived from this signalchannel; at a point between the pre-amplier 16 and the amplier 17, forexample. This signal is applied to the novel system provided by thepresent invention.

A record amplier 20 has applied thereto the diverted signal from thesignal output channel 15. This record d amplifier 20 is connected, to amagnetic recording head 21. An oscillator 22 is also connected to therecord head 21. The record amplifier 20 and the oscillator 22 cooperatein the well known manner to recordthe diverted signal from the signaloutput channel 15 uponia loop 23 of magnetic tape. Y Y

It is'desirable that a loop of magnetic tape is used in the presentapplication. However, any endless recording medium, or a recordingmedium of sumcient length may be a'suitable alternative. Y l

Y It isfurther desirable that the tape loop 23 is rotated at a constantvelocity and synchronisrn with the turntable 12. To this end one of therollers 2 7 which guides the tape loop 23 functions as a drive capstanand is associated'jwith a pressure roller 28. Thev capstan roller ismechanically coupled for rotation with the shaft 13 of the turntable 12as indicated bythe dashed line.

Two reproducing or playback heads 24 and 25 are magnetically coupled tothe tape loop 23. The first of these playbackV heads 24 is designated asplayback head (A). The second of these playback heads 25 is designatedas playback head (B). The playback heads 24 and 25 are separated by agiven distance, d, along the length ofthe vtapeloop 23. Because of theseparation of the heads 24 and 25 by the given distance,`d, the signalreproduced by playback head (B) is delayed from the Vsignal reproducedbyY the playback head (A). The delay between these signals ordinarilywill correspond tothe period of one revolution of the turntable V13.Therefore, vthe signal output from playback head (A) would correspond tothe signal reproduced by the pickup 14 fromk'one groove on the Vrecord10 and the output signal by playback head (B) Vwill correspond togthesignal reproduced by the pickup 14 atthe next, consecutive t 4 to ananalyzing circuit 35. This circuit 35 functions to prevent very shortperiods of identical signal output from the playback heads (A) and (B)from being identified as a repeated groove condition. The analyzingcircuit 35, therefore, insures only a repeated groove condition willproduce an output signal; Consequently, the output signal from theanalyzing circuit 35 may beused to indicate a repeated groove.

lt may be seen, therefore, from the above discussion that an identicalsignal reproduced by both playback heads (A) and (B) is indicative of arepeated groove condition. There is the remote contingency that in somepieces of music or speech recorded on a record, there may be two or moresilent grooves in which no signals are recorded. To this end, an errorcontrol circuit 36 is provided. The output of the error control circuitis an electrical signal that is applied to a mechanism 37 4 forcontrolling the pickup arm 14. The error control circuit functions toprevent the actuation of the pickup arm control mechanism 37 in theevent of consecutive silent grooves. An input signal for the errorcontrol circuit is derived from one of the amplifiers or 31. This inputis shown as being derived from the amplifier 31 in the drawing. rl`heVerror control circuit may in effect operate as a.safety switch toprevent an' output signal from the discriminator circuit 35 from beingapplied to the pickup arm control mechanism 37 during consecutive Ysilent grooves.

groove. The recording medium 23 functions asV an accu- Y raterandsensitive signal delay device.

An erase head 26 connected to the oscillator 23 is magneticallyrcoupledto the tape loop 23. This erase head 26'is7located at Va point on thetape loop after the playback head (B) and'before the record head 21 asviewed in the direction'of motion of the loop 23. The erase head 26operates in the well known manner to cancel informa- Ation signalsrecorded on the tape after these signals have been played back by theplayback heads 24 and 25, and before new signals are recordedron thetape by the record head 21'. Y Y Y It has been seen that the portion ofthesystem provided bythe present invention whichV is describedgabovesimultaneously provides two signals from consecutive grooves '0n-'thedisc record 10. The remaining portion of the 'system provided by thisinvention compares thesepsignals inforder to determine Whether arepeated groove condition ekistsi Y Y `An amplifier 30 is connected toreceive output signals from` the playback head (A) 24. `Anotheramplifier 31 is similarly connected to `the playback head (B) 25.Detectors 32V and 33 are connected to the ampliiiers 30 and 31respectively. These detectors 32 and 33 provide .an-output signal whichvaries more slowly than the signals directly reproduced by the playbackheads 24 and 2 5. These detectors 32 and 33 are in the nature ofenvelope detectorsy similar to those used in radio receivers. Itispreferable, but not every instance necessary, yto use 'such detectors.However, as a practical matter, they are useful to prevent imperfectionsin the recording medium, Vvsuch as minute gaps in the medium which causecollapsing'iields anddropouts, from adversely effecting the system.

r fThe output of the detectors 32 and 33 is connected to a comparingcircuit which may be a Vdifferential 'ampliiier 35;` The illustrativediierential amplifier 34 is designed .to provide anabsence of outputsignal when thesignals applied to it from the detectors 32 and 33 .ar'eidentical. 1 The outputof the differentialamplifler 34. dis applied Thepickup arm control mechanism V37 may be mechanically connected to thepickup 14 so that it may apply a force kto the pickup 14 and advance itacross the record 16B.' In its simplest form, the pickup arm controlmechanism may be a solenoid. For example, the solenoid may be disposedto actuate the reject mechanism of an automatic record changer so that arecord having repeating grooves will be automatically rejected.

A more detailed diagram of circuits suitable for the detectors 32 and33, the differential amplifier 34, the discriminator circuit 35 and theerrorcontrol circuit 36 are shownv in Figure 2. The operation ofthecircuits shown in Figure 2 will be best understood in connection withthe waveforms represented in Figure 3. The input terminals marked (A)and (B) correspond to the output of the amplifier 30 connected toplayback head (A) and the output of the amplifier 31 connected to theplayback Ahead (-B) respectively. Output (A) is connected to thevdetector network 32 through a capacitor 40. The detector network 32 maybe a well 4known type of envelope detector that produces a positivelypolarized output signal. It is shown as consisting of a shunt resistor41, a series diode 42, and a shunt capacitor 43 that is connectedbetween the output of the diode 42V and ground. A shunt resistor 44connected across the capacitor 43 also forms the grid resistor of thetube in the differential amplifier. The other input signals whichoriginateat the playback head (B) are applied through a capacitor 45 toan envelope detector 33 substantially identical to the envelope detector32 described above. A shunt resistor 46 is connected from one end of thecapacitor 45 to ground.

The input signal applied to the envelope detector 32 at input (A) isrepresented by Waveform (u) of Figure v3, and the input signal appliedto the other envelope detector 33 at input (B) is represented bywaveform (v) of Figure 3. It may be noted that these waveforms aretypical of music or speech; being composed of Waves which vary both infrequency and ofamplitude. However, it may further-be observed thatbefore a time designated as tr that both waveforms are different andthat yafter the time, designated as zr that both waveforms areidentical. V.This followsrfrom the fact that the signals represented byWaveform (u) are different from the signals Yrepresented by waveform (v)because they are reproduced at consecutive grooves. .At t1. i-t isassumed that a v,repetition of the same groove has occurred. The pickup14 may have jumped. Therefore, the Waves depicted are substantiallyidentical.

It has been found that correspondence of the output signals such asillustrated by waveforms (u) and (v) can be more easily established ifthese waves are detected by means of envelope detectors 32 and 33, suchas those illustrated in the drawing.

In waveform (w), the output of the envelope detectors 32 and 33 may beobserved and compared. The wave shown by the solid line may illustratethe output of the envelope detector 32. This wave would then appearacross the capacitor 43. The wave designated by the dashed line thenillustrates the output of the other envelope detector 33, and wouldappear across the shunt capacitor 46 contained therein. After time tr,the output of both envelope detectors are substantially identical sothat only one wave is represented. Y

A differential amplifier 33 may be used to compare the output signalsfrom the envelope detectors 32 and 33. This differential amplifier mayinclude two tubes 47 and 48 which have resistors 49 and S0 of equalvalue in the cathode circuits thereof and resistors 51 and 52 in theplate circuit thereof which also are of equal value. Of course, otherresistors and components (not shown for purposes of simplicity ofillustration) may be used to compensate for variations due to aging ofthe tubes 47 and 48 and due to stray impedances. A source of operatingvoltage, illustrated herein as being a battery 53, has its positiveterminal connected to the resistors 51 and 52 and its negative terminalconnected to ground. The operation of differential ampliiiers of thistype is well -known and it will be appreciated that identical signalsapplied to the grids of the tubes 47 and 48 will produce no outputsignal between the plates of the tubes. However, should the signalsapplied to the grids of one of the tubes be higher or lower in magnitudethan the signals applied to the grid of the other tube, an output signalwill appear between the plates of the tubes 47 and 48. Consequently, theplates of the tubes 47 and 43 in the differential amplifier 33 areconnected to the analyzing circuit 35.

The analyzing circuit 35 includes an arrangement of diodes in the formof a bridge 60. The plates of the tubes 47 and 48 are connected atopposite corners of the bridge 60. The remaining corners of the bridge60 are connected to opposite ends of a capacitor 61. A shunt resistor 62is connected across the capacitor 61. This resistor 62 forms the gridresistance of a tube 63. The capacitor 61 and the resistor 62 form aresistance-capacitance network having a predetermined discharge timeconstant. But, the bridge circuit 60, lthe capacitor 61, and theresistor 62 form a circuit having a very much shorter charging timeconstant.

It may be observed that the diodes in the bridge 60 arrangement arepolarized such that a negative voltage will develop at the terminal ofthe capacitor 61 that is connected to the grid of the tube 63.Consequently, as long as unequal signals are applied to the differentialampliiier 33 and an output therefrom results, a negative signal will bedeveloped across the capacitor 61. This signal is impressed upon thegrid of the tube 63.

Looking now to waveform (x) of Figure 3, the solid line represents thevoltage waveform established across the capacitor 61 as a result of thevariation in input signal applied to the diierential amplifier 33. Thedashed lines, some of which are obscured by the solid line, representthe output of the diiferential amplifier 33 which appears between theplates of the tubes 47 and 48. It is to be noted that there are shortintervals of no output signal due to brief periods when the envelopes ofthe input signals applied to the differential amplifier 33 areidentical. In order to discriminate such intervals from more prolongedintervals of identical signal which occur when a groove repeats, theresistance capacitance circuit 61, 62 having a short charging timeconstant, but a long discharging time constant is provided. It is to benoted that the capacitor maintains its charge over the short periods ofidentical envelope amplitude. However, the capacitor 61 has enough timeto discharge through its associated resistor 62 for the prolongedperiods during which no output signal is impressed across the bridgearrangement 60 by the dierential amplier. Therefore, the negative biasimpressed upon the grid of the tube that is connected to the capacitor61 is reduced suiiiciently to allow the tube 63 to conduct.

A source of voltage indicated illustratively as a battery 64 isconnected, at its negative terminal, to the cathode 63. The positive ofthe battery 64 is connected, through the operating winding 65 of a relay66, to the plate of the tube 63. Consequently, when the tube 63conducts, the relay 66 is operated and the contacts 67 thereof close.The pickup arm control mechanism 37 is connected to the movable one ofthe contacts 67. Since one side of the pickup arm control mechanism isgrounded, a circuit is completed through the contacts 67 and pickup armcontrol mechanism to ground. The fixed contact of the relay 66 isconnected through a normally closed pair of contacts 68 of another relay69. These contacts 68 are connected, in turn, to the positive terminalof the battery 53 which supplied operating power for thefdiiferentialamplifier 33. Consequently, when the contacts 67 of the relay 66 close,a complete circuit is provided from the battery 53 through the pickuparm control mechanism 37 The operation of the pickup arm controlmechanism is thereby effected.

The relay 69 and the contacts thereof 68 function as a safety switch inthe event that consecutive silent grooves occur which may erroneouslycause the operation of the pickup arm control mechanism 37. This relay69 is an element in the error control circuit 36 referred to inFigure 1. The error control circuit 36 includes a tube 70. The cathodeof this tube 70 is grounded, and the anode is connected through theoperating winding 71 of relay 69 to the positive terminal of the battery53. The grid of the tube 70 is connected to the input (B) by way of anenvelope detector network 72 which is similar to the envelope detectors32 and 33 heretofore described. However, the difference between thisenvelopedetector 72 and the other envelope detectors 32 and 33 that isthat the diode 73 therein is oppositely polarized; that is, the anode ofthe diode 73 is connected to the grid of the tube 70. Therefore, anegative voltage will be developed across the capacitor 74 when a signalis applied'to the envelope detector 72. The tube 70 will benonconductive so long as an inputl signal is applied at input (B). Thiswill occur when the playback head (B) picks up a signal from a tape loop23. In the event that a silent groove occurs, there will be an absenceof signal applied to the envelope detector 72. The tube 70and thecircuit thereof is designed in accordance with Well known engineeringprincipals so that tube 70 will be conductive when the negative biasapplied to the grid thereof is removed. Since the negative bias isremoved on the occurrence of a silent groove, the relay 69 will beoperated. This will cause the opening of the contact 68 of the relay 69.The circuit from the battery 53 to the pickup arm control mechanism 37will, therefore, be open and the operation of the pickup arm controlmechanism will be prevented.

Figure 4 illustrates a modified form of the present invention which issimilar in some respects to the system described in connection withFigures l, 2 and 3. Consequently, like reference numerals are used inFigure 4 to designate like parts shown in the other figures. A loop 23of magnetic tape is used. The reproduced signal is diverted Vfrom thesignal output channel 15, amplified, and applied to a record head 24 asin the above described system provided by the present invention. Asingle playback head 81 is positioned at a point separated from therecord head by the given distance, d.

. 32 which may be an envelope detector.

Y back head 81 will be delayed from the signal applied to the recordhead by aninterval equal to the period of one` revolution Vof therecord. An output signal from the record vampliier 29 is applied to anequalizing'network 80. Two signals corresponding to the signalreproduced l from the pickup 14 from two consecutive grooves are,

therefore, simultaneously available. The signal from the vleading grooveis available at the output of the record 33'which` may be an envelopedetector. The output of f the -detec'tor'is connected to a diierentialamplifier 34 forV comparing the -two simultaneous signals for identity.

' val equal to the period Yof one revolution of said record,

and means responsive to Said output signals operative to counteractrepetitive engagement of any one of said grooves byl said pickup device.

5. In phonograph apparatus for reproducing sound from grooved recordsincludinga pickup device for producing a signal output in response tosignals recorded in the grooves tracking said grooves, av systemtorcounteracting repetitive tracking of the same one of said grooves, saidsystemV comprising means electrically coupled to said pickup device andresponsive to the signal output 1 therefrom for delaying said signaloutput for a time intere 87 is applied to an i ampliiier 31. Theamplifier 31 is connected to a detector The equalizing network Si) isconnected to a detector The output of the envelope detector is thenvapplied to the diierential amplifier 34. rThe equalizing network 30 isprovided in order to` equalize the phase and amplitude characterisput.This equalization is desirable since the use of a magnetic taperecording-medium and an amplier 31 may'change the characteristics oftherecord amplier output signal.. Output ofthe record amplifier 29, the

output of the equalizing network 80 is also applied to Y an errorcontrol network 36.

the analyzing circuit 35 and the error control circuit .36

The detectors 32 and 33,

may be identical witht those described in connection with Figures 1 to3. It may be observed, however, one` input to the control circuit may beobtained from the equalizing network instead of from a playback head.This modified form of the present invention may be observed to utilize`fewer components than the system illustrated'in connection with Figure1.

There has, therefore, been described a new and improved system forpreventing repeated grooves on records. The records illustrated havebeen of the disc type.

pickup and means for electrically coupling said delay y means to saidelectrical means.

2. In phonograph apparatus for reproducing grooved records having apickup device engaging said grooves,

a system for detecting repeatedly reproduced signals recorded in asingle groove comprising means electricallyY coupled to said pickupdevice for-reproducing and comparing a pair of signals from consecutivegrooves of said record, means to delay one of said signals, and meansresponsive to said compared signals for sensing a repeated groovecondition. l

3. The phonograph apparatus and system, according to claim 1, comprisingin said first named means a me- A. dium upon which said signal output ofsaid pickup device may be re-recorded.`

4. In a phonograph apparatus wherein records having consecutive groovesare reproduced by a pickupv device engaging said grooves, a system forcounteracting repetitive engagement of the 'same one of saidgroovescomprisingrmeans electrically coupled to said pickup for pro- 1 viding.twooutput signals, said meansjncludingmmeans whereby said signals areseparated in time by an intertics ofV the VVsignal received from therecord amplifier out y Val equal to the period required Afor said pickupdevice to track one of said grooves, and means for comparing said`delayed signal and said undelayed signal for identity providing aresponse indicative of a repeated groove when said delayed and undelayedsignals are substantially identical for a given period, said signaloutput from said pick-up device and said signal output from saiddelaying means being applied to said comparing means.

6. In phonograph apparatus for the reproduction of sound from groovedrecords having a pickup device for tracking said grooves,traversing'said record, and transducing sound recorded therein intoelectrical signal; a system for eliminating the possibility ofrepetitively reproducing sound recorded in the'same one of said groovescomprising an auxiliary record medium; means for recording said'lelectrical signal on'said record medium; means for producing one of apair of signals correspond- Ying to said electrical signal; meansassociated with said record medium for reproducing the other of saidpair of signals Vseparated in time from said one produced signal by aninterval equal to the period required for said pickup device to track asingle one of said grooves; and means responsive to said pair ofelectrical signals for sensing a repeated groove.

. 7. In phonograph apparatus for the reproduction of sound from groovedrecords having a pickup device for tracking said grooves, traversingsaid record, and transducing sound recorded therein into electricalsignal; a system for eliminating the possibility of repetitivelyreproducing sound recorded in the same one of said grooves comprising anauxiliary record medium; means for recording said electrical signal ronysaid record medium; means associated with said record mediumrfo'rreproducing one of a pair of signals corresponding to said electricalsignal from said record medium; means associated with said record mediumfor reproducing the other of said pair of signals separated in time fromsaid one reproduced signal by an interval equal to the period requiredfor said pickup device to track a single one of said grooves; and meansresponsive to said pair of electrical signals for sensingV a repeatedgroove.

8..The phonograph apparatus and the system, according to claim 6 whereinsaid auxiliary recording medium in said system is a magnetic recordingmedium arranged in a loop, and wherein means 4are provided for rotatingsaid loop at a constant velocity.

Y 9. The phonograph apparatus and the system according to claim 8wherein said means associated Vwith said record medium in said systemcomprises a magnetic trans- -ducer electrically coupled to said pickupand magnetically coupled to said loop of magnetic recording medium forrecording said electrical signal from said pickup on said pickupproviding anelectrical signal corresponding to said recorded sound, asystem for eliminating the possibility of Af repetitive trackingoft'hensameV groove in saidl record by said pickup comprising a loopofinagnetic recording medium, means for rotating said loop at a constantvelocity, a magnetic recording head coupled to said pickup for recordingsaid electrical signal on said loop, a pair of magnetic reproducingheads positioned at points along said loop separated by a predetermineddistance from each other whereby one of said reproducing heads providesan output signal delayed by an interval equal to the period of onerevolution of said record from the output signal provided by the otherof said reproducing heads, means for erasing said signal recorded onsaid loop after reproduction by said reproducing heads, and meansresponsive to said output signals provided by said reproducing devicesfor sensing a repeated groove condition.

l1. In phonograph apparatus for the reproduction of sound from groovedrecords having a pickup device vfor tracking said grooves and traversingsaid record, said pickup providing an electrical signal corresponding tosaid recorded sound, a system for eliminating the possibility ofrepetitive tracking of the said groove in said record by said pickupcomprising, a loop of magnetic recording medium, means for rotating saidloop at a constant velocity, a magnetic recording head coupled to saidpickup for recording said electrical signal on said loop, a magneticreproducing head spaced in the direction of rotation of said loop fromsaid recording head, said recording head and said reproducing head beingsepaarted by a predetermined distance such that an output signal fromsaid reproducing head is delayed from said recorded electrical signal byan interval equal to the period of one revolution of said record, meansfor erasing said signal recorded on said loop after reproduction by saidreproducing head, and means responsive to said electrical signal fromsaid pickup and said delayed output signal from said reproducing head tosense a repeated groove condition.

12. In phonograph apparatus for playing grooved records having a pickupdevice for engaging said grooves, a system for eliminating thepossibility of said pickup repeatedly engaging the same groove of saidrecord comprising, means responsive to the signal output of said pickupdevice for providing two signals separated by a time interval equal tothe period of one revolution of said record, means for comparing saidtwo signals, and analyzing means coupled to said comparing means, saidanalyzing means being responsive to a repeated groove condition whensaid two signals applied to said comparing means are identical for agiven period.

13. In phonograph apparatus for playing grooved records having a pickupdevice for engaging said grooves, a system for eliminating thepossibility of said pickup repeatedly engaging the same groove of saidrecord comprising, means responsive to the signal output of said pickupdevice for providing two signals separated by a time interval equal to aperiod equal to one revolution of said record, means responsive to oneof said two signals for providing an output signal corresponding to theenvelope thereof, means responsive to the other of said two signals forproviding an output signal corresponding to the envelope thereof, meansfor comparing said envelopes of said two signals, and analyzing meanscoupled to said last named means, said analyzing means being responsiveto a repeated groove when said envelopes are identical for a givenperiod.

14. The apparatus and the system defined in claim 13, wherein saidsystem includes means electrically coupled to said analyzing means andcooperatively associated with said pickup for counteracting therepetitive engagement of any one of said grooves by said pickup.

15. In the system forming part of the phonograph apparatus as deiined inclaim 14, means for controlling the advance of said pickup across saidrecord, said pickup advance control means being coupled to saidanalyzing means, and means responsive to the condition that no recordedsignals exist in consecutive grooves of said record for inhibiting theoperation of said pickup control means.

16. In phonograph apparatus yfor the reproduction of sound yfrom groovedrecords having a pickup device for tracking said grooves and traversingsaid record, said pickup providing an electrical signal corresponding tosaid recorded sound, a system for eliminating the possibility ofrepetitive tracking of the same groove in said record by said pickupcomprising, a loop of magnetic recording medium, means for rotating saidloop at a constant velocity, a magnetic recording head coupled to saidpickup lfor recording said electrical signal on said loop, a pair cfmagnetic reproducing heads positioned at spaced points along said loop,said points being separated by a predetermined distance whereby one ofsaid reproducing heads provides an output signal delayed by an intervalequal to the period of one revolution of said record from the output`signal provided by the other of said reproducing heads, means forerasing said signal recorded on said loop after reproduction by saidreproducing heads, an envelope detector coupled to one of saidreproducing heads, another envelopedetector coupled to the other one ofsaid reproducing heads, a differential amplier having vdual inputs, saidinvelope detectors being individually coupled to a different one of said`dual inputs, an analyzing circuit including a network having adischarge time equal to a substantial portion of said period of onerevolution of said grooved record, means for applying the output signalfrom said differential amplifier to said analyzing circuit so as tooperate said network therein, pickup control means yfor advancing saidpickup across said record, said pickup control means being electricallycoupled to said analyzing circuit, and means responsive to Ithe outputsignal `from said analyzing circuit and to the envelope of the outputsignal from one of said reproducing heads for inhibiting the operationof said pickup advance control means during consecutive silent grooveson said record.

17. In phonograph apparatus for the reproduction of sound lfrom groovedrecords having a pickup device for tracking said grooves and traversingsaid record, said pickup providing an electrical signal corresponding tosaid recorded sound, a system for eliminating the possibility ofrepetitive tracking of any one groove on said record by said pickupcomprising, a loop of magnetic recording medium, means for rotating saidloop at a constant Velocity, a magnetic recording head coupled to saidpickup for recording said electrical signal on said loop, a magneticreproducing head spaced in the direction of rotation of said loop fromsaid recording head, said recording head and said reproducing head beingseparated by a predetermined distance such that an output signal fromsaid reproducing head is delayed for an interval equal to the period ofone revolution of said record, means for erasing said signal recorded onsaid loop after reproduction by said reproducing head, a network forequalizing the phase and amplitude response of said signal recorded onsaid loop with the output signal from said reproducing head, means forapplying said signal from said pickup device to said equalizing network,an envelope detector coupled to the output of said equalizing network,another envelope detector coupled to said reproducing head, adifferential ampliiier having dual inputs, said envelope detectors beingindividually coupled to a different one of said dual inputs, ananalyzing circuit including a network having a discharge time equal to asubstantial portion of the period of one revolution of said groovedrecord, means for applying the output signal from said diierentialamplifier to said analyzing circuit so as to operate said networktherein, pickup control means for advancing of said pickup across saidrecord, said pickup control means being electrically coupled to saidanalyzing circuit, and means responsive to the output signal from saidanalyzing circuit and to the envelope of the signal recorded on saidloop for inhibiting the operation of said pickupl control means duringconsecutive silent grooves on said record.

18. In lphonograph apparatus Afor reproducing sound from grooved recordsincluding a pickup device tracking said grooves, a system forcounteracting repetitive tracking of the same one of said grooves, saidsystem comprising means electrically coupled to said pickup device andresponsive to the signal output therefrom for providing a rst signal anda second signal both corresponding to said signal output from saidpickup device, said means being operative to delay said second signalwith respect to said rst signal for -a time interval equal to the periodrequired for said pickup device to track one of said grooves, and meansfor comparing said rst signal and said second signal for identityproviding a response in- 12 dicative of a repeated groove when saiddelayed and said undelayed signals are identical for a given period,said first signal and said second signal being applied to said comparingmeans.

References Cited in the file of this patent UNITED STATES PATENTS2,336,777 Clausen Dec. 14, 1943 2,375,525 Clausen May 8, 1945 2,674,660Ambrose Apr. 6, 1954 2,714,633 Fine a Aug. 2, 1955 2,846,519 MorrellAug. 5, 1958

